1. Field of the Invention
The present invention relates generally to a method and apparatus for transmitting broadcast data in a mobile communication system. More particularly, the present invention relates to a method and apparatus for transmitting and receiving broadcast data using outer-coding in a mobile communication system, provided to efficiently receive broadcast data transmitted using the outer-coding in a Code Division Multiple Access (CDMA) mobile communication system.
2. Description of the Related Art
A mobile communication system has developed from a system providing a voice service into a system capable of providing data services. The mobile communication system is now evolving into an advanced system capable of providing a broadcast service along with various data services. Such a system providing a broadcast service is currently undergoing various standardization negotiations in a 3rd Generation Partnership Project 2 (3GPP2) group using CDMA technology. In the CDMA2000 1x Rev. D standard, which is one of the standards proposed by the 3GPP2 group to provide a broadcast service, the broadcast service is called “Broadcast Multicast Service (BCMCS).” In addition to the CDMA2000 1x Rev. D standard, the 3GPP2 camp has established other standards to provide the broadcast service.
A description will now be made of a broadcast service defined in the CDMA2000 1x Rev. D standard. In the following description, the BCMCS service defined in the CDMA2000 1x Rev. D standard will be referred to as a “broadcast service.”
The broadcast service transmits block-interleaved frame-based broadcast data through one channel using a Time Domain Multiplex (TDM) scheme. The broadcast service can use Reed-Solomon coding which is error correction coding, also known as outer coding, in addition to inner coding, such as convolutional coding. In transmitting broadcast data, the use of the TDM scheme enables a receiver to receive a minimum number of selected frames when outer coding is not used therein, contributing to improved reception efficiency. However, in order to prevent a burst transmission error, Reed-Solomon coding is used, and the use of the Reed-Solomon coding is proposed in the CDMA2000 1x Rev. D standard.
A detailed description will now be made of a broadcast data transmission scheme currently proposed for the broadcast service.
FIG. 1 is a timing diagram for a description of a process providing a broadcast service with a TDM scheme according to the CDMA2000 1x Rev. D standard.
In FIG. 1, A, B, C, and D represent the types of broadcast services. In order to provide broadcast services, a base station (BS) time-domain-multiplexes the broadcast services before transmission to subscriber stations (SSs) as illustrated in FIG. 1. The broadcast services, which are time-domain-multiplexed before being transmitted, have a TDM period (TDM_PERIOD) 100. A plurality of TDM slots are allocated to the TDM period 100, and a plurality of TDM periods constitute one TDM super period.
The TDM period and the TDM super period will be described from the viewpoint of a service provided. If a subscriber station desires to receive a particular broadcast service, it can check the types of broadcast services that are transmitted through a predetermined channel after being time-domain-multiplexed. After checking the types of the broadcast services in this way, if a user of the subscriber station desires to watch and/or listen to a particular broadcast service, the subscriber station generates a message for requesting the broadcast service selected by the user and transmits the request message to a base station. In response, the base station generates information used for receiving the broadcast services which are transmitted after being time-domain-multiplexed as illustrated in FIG. 1, and transmits the generated information to the subscriber station. The generated information used for receiving the broadcast services, which are provided after being time-domain-multiplexed, is transmitted using a message format of Table 1. Tables 2 and 3 are provided to further describe the information transmitted using the message format of Table 1.
TABLE 1Message FieldNumber of BitsTDM_USED_IND1TDM_SLOT_LENGTH0 or 2TDM_PERIOD0 or 2TDM_MASK0 or (4, 8, or 16)TDM_SUPER_PERIOD_MASK0 or 4
In Table 1, a TDM_USED_IND field is comprised of 1 bit and indicates whether a provided broadcast service is transmitted after being time-domain-multiplexed. If broadcast service data is transmitted after being time-domain-multiplexed, the succeeding values are added. Therefore, if the fields, other than the TDM_USED_IND field, illustrated in Table 1 have 0 number of bits, it means that Time Domain Multiplexing is not used. In addition, a TDM_SLOT_LENGTH field 110 has a 2-bit value when Time Domain Multiplex is used, and as illustrated in FIG. 1, it indicates a length of time included in one TDM period 100. A TDM_PERIOD field of Table 1 indicates the number of slots included in the TDM period 100, and has a 2-bit value when Time Domain Multiplex is used. In addition, a TDM_MASK field has a value using 4 bits, 8 bits or 16 bits, and indicates a specific slot in the TDM period 100, in which a broadcast service requested by the user is included. In FIG. 1, an example in which the TDM_MASK field has a 4-bit value is shown by reference numeral 120. Finally, in Table 1, a TDM_SUPER_PERIOD_MASK field has a value of 0 bits or 4 bits according to whether or not a super frame period is used. The TDM_SUPER_PERIOD_MASK field has a 4-bit value when the super frame period is used, and an example thereof is shown by reference numeral 130 in FIG. 1.
Table 2 illustrates a matching relation between the TDM_SLOT_LENGTH parameter values and the TDM_PERIOD parameter values when the information of Table 1 is transmitted.
TABLE 2TDM_SLOT—LENGTHLength of the TDMTDM_PERIOD(binary)slot(binary)TDM Period0020 ms00 4 slots0140 ms01 8 slots1080 ms1016 slots11Reserved11Reserved
In the TDM_SLOT_LENGTH field, ‘Reserved’ means that a corresponding parameter is unused. Table 3 illustrates a matching relation between the TDM periods and the TDM slot lengths.
TABLE 3TDM PeriodSlot Length4 slots8 slots16 slots20 ms (1 frame)16 frames (I) 32 frames (II) 64 frames (III)40 ms (2 frames)32 frames (IV) 64 frames (V)128 frames (VI)80 ms (4 frames)64 frames (VII)128 frames (VIII)256 frames (IX)
Table 3 illustrates a matching relation between the number of slots included in a TDM period and the number of frames transmitted within each TDM period according to a slot length. As can be understood from Table 3, the possible number of transmitted frames becomes a minimum of 16 frames up to a maximum of 256 frames according to the number (4, 8 or 16) of slots in the TDM period 100 and the slot length (20, 40 or 80 ms).
Once a subscriber station receives the information of Table 1, it can receive data of a corresponding frame. A detailed description thereof will now be made with reference to FIG. 1. If a particular user desires to receive a broadcast service A, for instance, a value denoted by reference numeral 121 is transmitted as a TDM_MASK value of Table 1. A value ‘1010’ is transmitted as a TDM_MASK value, which is transmitted to a subscriber station desiring to listen to the broadcast service A. In this way, a value ‘0100’ denoted by reference numeral 122, for instance, will be transmitted as a TDM_MASK value, which is transmitted to a subscriber station desiring to listen to a broadcast service B. A value ‘0001’ denoted by reference numeral 123, for instance, will be transmitted as a TDM_MASK value which is transmitted to a subscriber station desiring to listen to a broadcast service C. A value ‘1010’ denoted by reference numeral 124, for instance, will be transmitted as a TDM_MASK value, which is transmitted to a subscriber station desiring to listen to a broadcast service D.
The TDM_MASK for the broadcast service A and the TDM_MASK for the broadcast service D indicate that the broadcast service A and the broadcast service D are transmitted in a crossing way at the same reception point, and this is distinguished by a TDM_SUPER_PERIOD_MASK value. That is, for the broadcast services A, B, C and D, TDM_SUPER_PERIOD_MASK values are set as shown by reference numeral 130, and reference numerals 131, 132, 133, and 134 indicate corresponding broadcast services transmitted for certain TDM periods.
The CDMA2000 1x Rev. D standard calls for Reed-Solomon scheme-based outer coding to be used with a broadcast service. The Reed-Solomon scheme-based outer coding is performed at 64-frame periods as defined in a BCMCS physical layer standard, and the 64 frames are encoded through 4 sub-buffers before being transmitted. With reference to FIG. 2, a description will now be made of a broadcast service scheme using the Reed-Solomon scheme-based outer coding.
FIG. 2 is a diagram illustrating the operation Reed-Solomon encoding as outer coding of broadcast service data according to the CDMA2000 1x Rev. D standard.
In FIG. 2, 4 sub-buffers sub-buffer#0 (210), sub-buffer#1 (220), sub-buffer#2 (230) and sub-buffer#3 (240) are illustrated as defined in the standard. Because the Reed-Solomon encoding is performed at 64-frame periods as defined in the BCMCS physical layer standard, the 4 sub-buffers 210, 220, 230 and 240 have a structure capable of storing a total of 64 frames. Therefore, each of the sub-buffers 210, 220, 230 and 240 is constructed such that it can store 16 frames. Actually, however, the number of frames stored in each of the sub-buffers 210, 220, 230 and 240 is set to a predetermined number k (where k is an integer which is smaller than 16), in order to perform Reed-Solomon encoding. Therefore, k frames are stored in first k areas of each of the sub-buffers 210, 220, 230 and 240, and the remaining areas of each of the sub-buffers 210, 220, 230 and 240 are empty. Parity frames which are Reed-Solomon encoded frames are stored in the empty areas. In this manner, 16 frames are filled in each of the sub-buffers 210, 220, 230 and 240.
This process is shown as a Reed-Solomon (RS) encoding process in FIG. 2. That is, reference numerals 211, 221, 231 and 241 of FIG. 2 illustrate the buffer states after the Reed-Solomon encoding is performed. The sub-buffers 211, 221, 231 and 241 including the Reed-Solomon encoded frames perform sequential outputting. That is, after a first frame output from the first sub-buffer 211 is transmitted, a first frame from the second sub-buffer 221 is transmitted, and then a first frame of the third sub-buffer 231 is transmitted. Finally, after a first frame of the fourth sub-buffer 241 is transmitted, a second frame of the first sub-buffer 211 is transmitted.
Illustrated in the right-hand side of FIG. 2 is the transmission order of the frames stored in the sub-buffers 211, 221, 231 and 241, for the convenience of description. That is, reference numeral 212 represents the transmission order of the frames stored in the sub-buffer 211, reference numeral 222 represents the transmission order of the frames stored in the sub-buffer 221, reference numeral 232 represents the transmission order of the frames stored in the sub-buffer 231, and reference numeral 242 represents the transmission order of the frames stored in the sub-buffer 241. For example, regarding the first sub-buffer 211, a first frame is transmitted firstly, a second frame is transmitted fifthly, and a third frame is transmitted ninthly. Also, the frames stored in the other sub-buffers 221, 231 and 241 are transmitted in the same method.
With reference to FIG. 3, a description will now be made of an example in which the frames are transmitted in a TDM super period and a TDM period.
FIG. 3 is a timing diagram for transmission of broadcast service data in a case where data for 6 broadcast services is transmitted using the TDM/Reed-Solomon scheme. Referring to FIG. 3, a TDM super period 300 includes 4 TDM periods 310, 320, 330 and 340. Broadcast service frames A, B, C, D, E and F for different broadcast services are transmitted for the respective TDM periods 310, 320, 330 and 340.
When a subscriber station, or a reception side, receives the frames transmitted in the manner illustrated in FIG. 3, the subscriber station should receive data per each sub-buffer for a corresponding sub-block. Further, the subscriber station should receive not only the frames for its own broadcast service but also the frames for other broadcast services, transmitted through the corresponding sub-buffer, in order to enable decoding. The reason why the subscriber station receives not only the frames for its own broadcast service but also the frames for other broadcast services through the same sub-buffer is because the Reed-Solomon scheme is used as outer coding as described above with reference to FIG. 2. This will be described in more detail with reference to FIG. 4.
FIG. 4 is a diagram illustrating the respective sub-buffers in which transmission data for the broadcast services provided in the method of FIG. 2 is stored.
Referring to FIG. 4, transmission frame data is stored in first to fourth sub-buffers 410, 420, 430 and 440. It is assumed that FIG. 4 is equal to FIG. 3 in terms of a data transmission method. For example, the frames for 3 broadcast services A, E and F are stored in the first sub-buffer 410, the frames for 3 broadcast services A, B and F are stored in the second sub-buffer 420, the frames for 2 broadcast services C and F are stored in the third sub-buffer 430, and the frames for 2 broadcast services D and F are stored in the fourth sub-buffer 440. The last several frames for the respective sub-buffers 410, 420, 430 and 440 are stored as parity frames for Reed-Solomon encoding.
Therefore, a subscriber station desiring to receive a particular broadcast service cannot actually enjoy the advantage of TDM due to the multiple broadcast service frames transmitted in the foregoing manner. That is, the subscriber station cannot perform Reed-Solomon decoding unless it receives the full data in sub-buffers for the corresponding sub-blocks through which its desired broadcast service is transmitted.
Therefore, in the broadcast service to which the outer coding is applied, the subscriber station will unnecessarily receive other broadcast services in order to receive a particular service.